linux-kernel - Re: [PATCH v8 2/3] drm/panel: startek-kd070fhfid015: add another init step

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Message-ID: <d70b62f8-e24e-4a10-8c6b-18d2e19f1337@collabora.com>
Date: Thu, 20 Mar 2025 13:37:49 +0100
From: AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>
To: Alexandre Mergnat <amergnat@...libre.com>,
 Catalin Marinas <catalin.marinas@....com>, Will Deacon <will@...nel.org>,
 Neil Armstrong <neil.armstrong@...aro.org>,
 Jessica Zhang <quic_jesszhan@...cinc.com>,
 Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
 Maxime Ripard <mripard@...nel.org>, Thomas Zimmermann <tzimmermann@...e.de>,
 David Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>,
 Chun-Kuang Hu <chunkuang.hu@...nel.org>,
 Philipp Zabel <p.zabel@...gutronix.de>,
 Matthias Brugger <matthias.bgg@...il.com>
Cc: linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
 dri-devel@...ts.freedesktop.org, linux-mediatek@...ts.infradead.org
Subject: Re: [PATCH v8 2/3] drm/panel: startek-kd070fhfid015: add another init
 step

Il 20/03/25 09:48, Alexandre Mergnat ha scritto:
> Currently, the panel set power, set gpio and enable the display link
> in stk_panel_prepare, pointed by drm_panel_funcs.prepare, called by
> panel_bridge_atomic_pre_enable, pointed by
> drm_bridge_funcs.atomic_pre_enable. According to the drm_bridge.h,
> atomic_pre_enable must not enable the display link
> 
> Since the DSI driver is properly inited by the DRM, the panel try to
> communicate with the panel before DSI is powered on.
> 

The panel driver shall still be able to send commands in the .prepare() callback
and if this is not happening anymore... well, there's a problem!

> To solve that, use stk_panel_enable to enable the display link because
> it's called after the mtk_dsi_bridge_atomic_pre_enable which is power
> on the DSI.
> 
> Signed-off-by: Alexandre Mergnat <amergnat@...libre.com>
> ---
>   .../gpu/drm/panel/panel-startek-kd070fhfid015.c    | 25 +++++++++++++---------
>   1 file changed, 15 insertions(+), 10 deletions(-)
> 
> diff --git a/drivers/gpu/drm/panel/panel-startek-kd070fhfid015.c b/drivers/gpu/drm/panel/panel-startek-kd070fhfid015.c
> index c0c95355b7435..bc3c4038bf4f5 100644
> --- a/drivers/gpu/drm/panel/panel-startek-kd070fhfid015.c
> +++ b/drivers/gpu/drm/panel/panel-startek-kd070fhfid015.c
> @@ -135,19 +135,9 @@ static int stk_panel_prepare(struct drm_panel *panel)
>   	gpiod_set_value(stk->enable_gpio, 1);
>   	mdelay(20);
>   	gpiod_set_value(stk->reset_gpio, 1);
> -	mdelay(10);
> -	ret = stk_panel_init(stk);
> -	if (ret < 0)
> -		goto poweroff;

Also, you're moving both init and set_display_on to the enable callback...
this is suboptimal.

You should do the DrIC setup in .prepare() (can include SLEEP OUT), and then you
should have a .enable() callback that calls DISP ON, a .disable() callback that
calls DISP OFF, and .unprepare() that turns everything off.

Cheers,
Angelo

> -
> -	ret = stk_panel_on(stk);
> -	if (ret < 0)
> -		goto poweroff;
>   
>   	return 0;
>   
> -poweroff:
> -	regulator_disable(stk->supplies[POWER].consumer);
>   iovccoff:
>   	regulator_disable(stk->supplies[IOVCC].consumer);
>   	gpiod_set_value(stk->reset_gpio, 0);
> @@ -156,6 +146,20 @@ static int stk_panel_prepare(struct drm_panel *panel)
>   	return ret;
>   }
>   
> +static int stk_panel_enable(struct drm_panel *panel)
> +{
> +	struct stk_panel *stk = to_stk_panel(panel);
> +	int ret;
> +
> +	ret = stk_panel_init(stk);
> +	if (ret < 0)
> +		return ret;
> +
> +	ret = stk_panel_on(stk);
> +
> +	return ret;
> +}
> +
>   static const struct drm_display_mode default_mode = {
>   		.clock = 163204,
>   		.hdisplay = 1200,
> @@ -239,6 +243,7 @@ drm_panel_create_dsi_backlight(struct mipi_dsi_device *dsi)
>   }
>   
>   static const struct drm_panel_funcs stk_panel_funcs = {
> +	.enable = stk_panel_enable,
>   	.unprepare = stk_panel_unprepare,
>   	.prepare = stk_panel_prepare,
>   	.get_modes = stk_panel_get_modes,
>